Customers who have bought the 340g tins, with any date code, have been urged not to eat the corned beef but to return it to the supermarket.

Asda withdrew the product on March 8 after it was found to contain more than 1% horse DNA. Bute was detected in some samples, at the level of four parts per billion (4ppb), when further tests were carried out.

The corned beef is the only meat product in which bute has been found, according to the FSA. It said no other Asda products are thought to be affected and that customers who bought the corned beef should contact the supermarket for a refund. They said that while animals treated with bute should not enter the food chain, the risk of damage to the health of anyone who had eaten such meat is "very low".

Chief Medical Officer Professor Dame Sally Davies previously said: "Horse meat containing phenylbutazone presents a very low risk to human health. Phenylbutazone, known as bute, is a commonly used medicine in horses. It is also prescribed to some patients who are suffering from a severe form of arthritis."

In a statement on the Asda website, the supermarket said it was also recalling tins of Chosen By You corned beef. "The tinned Chosen By You Corned Beef (340g) product, also withdrawn in March, has not tested positive for phenylbutazone," the statement read. However as a precaution it is also being recalled as it is made in the same factory."

Asda claimed to have taken "an extremely cautious approach since the very beginning" and had carried out more than 700 tests so far, "moving swiftly to remove any products" when they had any concerns.

In a separate development today, the FSA said that two more beef products had been found to contain horse DNA as part of the UK-wide sampling they had undertaken. The FSA confirmed results for four of the remaining five samples tested under the programme, adding that all five products had already been removed from sale.

Neither of the two samples containing horse DNA at or above the 1% threshold for reporting - a burger bought from Nefyn Pizza and Kebab House in Gwynedd and manufactured by the Burger Manufacturing Company and a beefburger bought from Pig Out in Walsall and manufactured by King Fry Meat Products - were found to contain bute or pig DNA. There is one result yet to be reported.